| Message ID | 20230125203743.564009-1-jim.cromie@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | fix DRM_USE_DYNAMIC_DEBUG regression | expand |
On Wed, 25 Jan 2023, Jim Cromie <jim.cromie@gmail.com> wrote: > Hi everyone, > > In v6.1 DRM_USE_DYNAMIC_DEBUG=y has a regression enabling drm.debug in > drivers at modprobe. I realize we haven't actually addressed the regression in any way yet, and any distro enabling DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE will have DRM_USE_DYNAMIC_DEBUG=y by default, and we're hitting the issue with trying to gather logs from users on v6.1 or later. It hampers debugging pretty badly. I appreciate the effort in fixing the problem properly here, but we'll need a fix that we can backport to stable kernels. Maybe just Ville's idea of config DRM_USE_DYNAMIC_DEBUG bool "use dynamic debug to implement drm.debug" - default y + default n + depends on BROKEN depends on DRM depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE but we'll need that as a patch and merged and backported ASAP. In the mean time, is there a workaround that the user could enable, say, on the kernel command line, to enable drm debugs on driver kernel modules, all the way from boot? BR, Jani. > > It is due to a chicken-egg problem loading modules; on `modprobe > i915`, drm is loaded 1st, and drm/parameters/debug is set. When > drm_debug_enabled() tested __drm_debug at runtime, this just worked. > > But with DRM_USE_DYNAMIC_DEBUG=y, the runtime test is replaced with a > static_key for each drm_dbg/dyndbg callsite, enabled by dyndbg's > kparam callback on __drm_debug. So with drm.ko loaded and initialized > before the dependent modules, their debug callsites aren't yet present > to be enabled. > > STATUS - v3 > > not quite ready. > rebased on -rc5, hopefully applies to patchwork head > still has RFC patch -> CI_ONLY temporary, to avoid panics > boots on my amdgpu box, drm.debug=0x3ff works at boot-time > the "toggled" warning is repeatable with test_dynamic_debug*.ko > it also occurs on amdgpu, so not just artificial. > v2 is https://lore.kernel.org/lkml/20230113193016.749791-1-jim.cromie@gmail.com/ > > OVERVIEW > > As Jani Nikula noted rather more gently, DECLARE_DYNDBG_CLASSMAP is > error-prone enough to call broken: sharing of a common classmap > required identical classmap definitions in all modules using DRM_UT_*, > which is inherently error-prone. IOW, it muddled the K&R distinction > between a (single) definition, and multiple references. > > So patches 10-13 split it into: > > DYNDBG_CLASSMAP_DEFINE used once per subsystem to define each classmap. > DYNDBG_CLASSMAP_USE declare dependence on a DEFINEd classmap. > > DYNDBG_CLASSMAP_DEFINE initializes the classmap, stores it into the > (existing) __dyndbg_classes section, and exports the struct var > (unlike DECLARE_DYNDBG_CLASSMAP). > > DYNDBG_CLASSMAP_USE initializes a class-ref struct, containing the > user-module-name, and a ref to the exported classmap var. > > The distinction allows separate treatment of classmaps and > classmap-refs, the latter getting additional behavior to propagate > parent's kparam settings to USEr. (forex: drm.debug to drm-drivers) > > . lookup the classmap defn being referenced, and its module > . find the module's kernel-params using the classmap > . propagate kparam vals into the prdgs in module being added. > > It also makes the weird coordinated-changes-by-identical-classmaps > "feature" unnecessary. > > Patch-10 splits the DECLARE macro into DEFINE & USE, and updates uses. > > Patch-11 is the core of it; the separate treatment begins in > ddebug_add_module(). It calls ddebug_attach_module_classes(1) to > handle class-defns; this adds ddebug_attach_client_module_classes(2) > to handle class-refs, as they are found while modprobing drm > drivers. (2) calls ddebug_apply_parents_params(3) on each USEr's > referred classmap definition. > > (3) scans kernel-params owned by the module DEFINEing the classmap, > either builtin or loadable, calls ddebug_match_apply_kparam(4) on each. > > (4) looks for kparams which are wired to dyndbg's param-ops. Those > params have a struct ddebug_class_param attached, which has a classmap > and a ref to a state-var (__drm_debug for DRM case). If the kparam's > classmap is the same as from (2), then apply its state-var to the > client module by calling ddebug_apply_class_bitmap(). > > Patch-12 cleans up DYNDBG_CLASSMAP_USE, dropping now unneeded args. > > Patch-13 improves DYNDBG_CLASSMAP_DEFINE, by accepting DRM_UT_* > symbols directly, not "DRM_UT_*" (their strings). It adds new > include/linux/map.h to support this. > > Patches 1-9 are prep, refactor, cleanup, tighten interfaces > > Patches 15-18 extend test_dynamic_debug to recreate DRM's multi-module > regression; it builds both test_dynamic_debug.ko and _submod.ko, with > an ifdef to _DEFINE in the main module, and _USE in the submod. This > gives both modules identical set of prdbgs, which is helpful for > comparing results. > > here it is, working properly: > > doing class DRM_UT_CORE -p > [ 9904.961750] dyndbg: read 21 bytes from userspace > [ 9904.962286] dyndbg: query 0: "class DRM_UT_CORE -p" mod:* > [ 9904.962848] dyndbg: split into words: "class" "DRM_UT_CORE" "-p" > [ 9904.963444] dyndbg: op='-' flags=0x0 maskp=0xfffffffe > [ 9904.963945] dyndbg: parsed: func="" file="" module="" format="" lineno=0-0 class=DRM_UT_CORE > [ 9904.964781] dyndbg: good-class: drm.DRM_UT_CORE module:drm nd:302 nc:1 nu:0 > [ 9904.966411] dyndbg: class-ref: drm_kms_helper.DRM_UT_CORE module:drm_kms_helper nd:95 nc:0 nu:1 > [ 9904.967265] dyndbg: class-ref: drm_display_helper.DRM_UT_CORE module:drm_display_helper nd:150 nc:0 nu:1 > [ 9904.968349] dyndbg: class-ref: i915.DRM_UT_CORE module:i915 nd:1659 nc:0 nu:1 > [ 9904.969801] dyndbg: class-ref: amdgpu.DRM_UT_CORE module:amdgpu nd:4425 nc:0 nu:1 > [ 9904.977079] dyndbg: class-ref: nouveau.DRM_UT_CORE module:nouveau nd:103 nc:0 nu:1 > [ 9904.977830] dyndbg: processed 1 queries, with 507 matches, 0 errs > doing class DRM_UT_DRIVER +p > [ 9906.151761] dyndbg: read 23 bytes from userspace > [ 9906.152241] dyndbg: query 0: "class DRM_UT_DRIVER +p" mod:* > [ 9906.152793] dyndbg: split into words: "class" "DRM_UT_DRIVER" "+p" > [ 9906.153388] dyndbg: op='+' flags=0x1 maskp=0xffffffff > [ 9906.153896] dyndbg: parsed: func="" file="" module="" format="" lineno=0-0 class=DRM_UT_DRIVER > [ 9906.154746] dyndbg: good-class: drm.DRM_UT_DRIVER module:drm nd:302 nc:1 nu:0 > [ 9906.155433] dyndbg: class-ref: drm_kms_helper.DRM_UT_DRIVER module:drm_kms_helper nd:95 nc:0 nu:1 > [ 9906.156267] dyndbg: class-ref: drm_display_helper.DRM_UT_DRIVER module:drm_display_helper nd:150 nc:0 nu:1 > [ 9906.157365] dyndbg: class-ref: i915.DRM_UT_DRIVER module:i915 nd:1659 nc:0 nu:1 > [ 9906.163848] dyndbg: class-ref: amdgpu.DRM_UT_DRIVER module:amdgpu nd:4425 nc:0 nu:1 > [ 9906.178963] dyndbg: class-ref: nouveau.DRM_UT_DRIVER module:nouveau nd:103 nc:0 nu:1 > [ 9906.179934] dyndbg: processed 1 queries, with 1286 matches, 0 errs > > > Patch-19 is a *workaround* for a panic: __jump_label_patch can "crash > the box" when the jump-entry is in the wrong state. The current code > makes no distinction between a well-formed "toggled" state and an > "insane" state. Not for keeps. > > It fixes mis-initialization problems like this: > > [ 1594.032504] dyndbg: query 0: "class D2_DRIVER -p" mod:* > [ 1594.032823] dyndbg: split into words: "class" "D2_DRIVER" "-p" > [ 1594.033183] dyndbg: op='-' flags=0x0 maskp=0xfffffffe > [ 1594.033507] dyndbg: parsed: func="" file="" module="" format="" lineno=0-0 class=D2_DRIVER > [ 1594.034014] dyndbg: good-class: test_dynamic_debug.D2_DRIVER module:test_dynamic_debug nd:32 nc:4 nu:0 > [ 1594.034695] dyndbg: changed lib/test_dynamic_debug.c:156 [test_dynamic_debug]do_cats p => _ > [ 1594.035304] dyndbg: class-ref: test_dynamic_debug_submod.D2_DRIVER module:test_dynamic_debug_submod nd:32 nc:0 nu:4 > [ 1594.036052] jump_label: found toggled op at do_cats+0x16/0x180 [test_dynamic_debug_submod] [00000000ff2582ac] (0f 1f 44 00 00 != e9 e1 00 00 00)) size:5 type:0 > [ 1594.037036] dyndbg: changed lib/test_dynamic_debug.c:156 [test_dynamic_debug_submod]do_cats p => _ > [ 1594.037604] dyndbg: processed 1 queries, with 2 matches, 0 errs > [ 1594.037968] dyndbg: bit_1: 2 matches on class: D2_DRIVER -> 0x0 > > These errors are reliably reproduced by a shell-func which modprobes > (with the right args) the test mod & submod.ko (in the commit message). > > So this isnt really ready for inclusion, but Id like to send the whole > set to the CI-gym for a workout. The RFC/for-TESTING patch will > mitigate panics, and still be detectable. > > Besides, Murphys law requires I publish some error before I can make progress. > > > Jim Cromie (19): > test-dyndbg: fixup CLASSMAP usage error > test-dyndbg: show that DEBUG enables prdbgs at compiletime > dyndbg: replace classmap list with a vector > dyndbg: make ddebug_apply_class_bitmap more selective > dyndbg: split param_set_dyndbg_classes to inner/outer fns > dyndbg: drop NUM_TYPE_ARRAY > dyndbg: reduce verbose/debug clutter > dyndbg: tighten ddebug_class_name() 1st arg > dyndbg: constify ddebug_apply_class_bitmap args > dyndbg-API: split DECLARE_(DYNDBG_CLASSMAP) to $1(_DEFINE|_USE) > dyndbg-API: specialize DYNDBG_CLASSMAP_(DEFINE|USE) > dyndbg-API: DYNDBG_CLASSMAP_USE drop extra args > dyndbg-API: DYNDBG_CLASSMAP_DEFINE() improvements > drm_print: fix stale macro-name in comment > test-dyndbg: build test_dynamic_debug_submod > test-dyndbg: rename DD_SYS_WRAP to DYNDBG_CLASSMAP_PARAM > test-dyndbg: disable WIP dyndbg-trace params > test-dyndbg: tune sub-module behavior > jump_label: RFC / temporary for CI - tolerate toggled state > > arch/x86/kernel/jump_label.c | 24 ++- > drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 14 +- > drivers/gpu/drm/display/drm_dp_helper.c | 14 +- > drivers/gpu/drm/drm_crtc_helper.c | 14 +- > drivers/gpu/drm/drm_print.c | 22 +- > drivers/gpu/drm/i915/i915_params.c | 14 +- > drivers/gpu/drm/nouveau/nouveau_drm.c | 14 +- > include/asm-generic/vmlinux.lds.h | 1 + > include/drm/drm_print.h | 6 +- > include/linux/dynamic_debug.h | 57 ++++-- > include/linux/map.h | 55 +++++ > kernel/module/main.c | 3 + > lib/Makefile | 3 +- > lib/dynamic_debug.c | 258 ++++++++++++++++++------ > lib/test_dynamic_debug.c | 118 +++++++---- > lib/test_dynamic_debug_submod.c | 10 + > 16 files changed, 437 insertions(+), 190 deletions(-) > create mode 100644 include/linux/map.h > create mode 100644 lib/test_dynamic_debug_submod.c
On Fri, Feb 03, 2023 at 11:34:02AM +0200, Jani Nikula wrote: > On Wed, 25 Jan 2023, Jim Cromie <jim.cromie@gmail.com> wrote: > > Hi everyone, > > > > In v6.1 DRM_USE_DYNAMIC_DEBUG=y has a regression enabling drm.debug in > > drivers at modprobe. > > I realize we haven't actually addressed the regression in any way yet, > and any distro enabling DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE will have > DRM_USE_DYNAMIC_DEBUG=y by default, and we're hitting the issue with > trying to gather logs from users on v6.1 or later. It hampers debugging > pretty badly. > > I appreciate the effort in fixing the problem properly here, but we'll > need a fix that we can backport to stable kernels. > > Maybe just Ville's idea of > > config DRM_USE_DYNAMIC_DEBUG > bool "use dynamic debug to implement drm.debug" > - default y > + default n > + depends on BROKEN > depends on DRM > depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE > > but we'll need that as a patch and merged and backported ASAP. +1 for this Regards Stanislaw